Increased extinction potential of insular fish populations with reduced life history variation and low genetic diversity.

Hellmair M, Kinziger AP - PLoS ONE (2014)

Bottom Line:
We illustrate that, for this annual species, continuous reproduction is a safeguard against reproductive failure by any one population segment, as natural, stochastically driven salinity increases frequently result in high mortality among juvenile individuals.Notably, we found a significant correlation between genetic diversity and demographic variation in the study populations, which could be the result of population stressors that restrict both of these diversity measures simultaneously, or suggestive of a causative relationship between these population characteristics.These findings demonstrate the importance of biocomplexity at the population level, and assert that the maintenance of diversity contributes to population resilience and conservation of this endangered species.

Affiliation: Department of Fisheries Biology, Humboldt State University, Arcata, California, United States of America; FISHBIO, Chico, California, United States of America.

ABSTRACTTheoretical work has shown that reduced phenotypic heterogeneity leads to population instability and can increase extinction potential, yet few examples exist of natural populations that illustrate how varying levels expressed diversity may influence population persistence, particularly during periods of stochastic environmental fluctuation. In this study, we assess levels of expressed variation and genetic diversity among demographically independent populations of tidewater goby (Eucyclogobius newberryi), show that reductions in both factors typically coincide, and describe how low levels of diversity contribute to the extinction risk of these isolated populations. We illustrate that, for this annual species, continuous reproduction is a safeguard against reproductive failure by any one population segment, as natural, stochastically driven salinity increases frequently result in high mortality among juvenile individuals. Several study populations deviated from the natural pattern of year-round reproduction typical for the species, rendering those with severely truncated reproductive periods vulnerable to extinction in the event of environmental fluctuation. In contrast, demographically diverse populations are more likely to persist through such periods through the continuous presence of adults with broader physiological tolerance to abrupt salinity changes. Notably, we found a significant correlation between genetic diversity and demographic variation in the study populations, which could be the result of population stressors that restrict both of these diversity measures simultaneously, or suggestive of a causative relationship between these population characteristics. These findings demonstrate the importance of biocomplexity at the population level, and assert that the maintenance of diversity contributes to population resilience and conservation of this endangered species.

Mentions:
We detected a correlation between the temporal extent of the reproductive season and genetic diversity. A significant proportion of the variation in demography (as measured by observed size ranges and SD) was explained by expected heterozygosity (p = 0.018 and 0.022, respectively) after accounting for the effects of habitat area in a general liner model analysis (model: range(mm)/SD = log10(hectares)+HE). Similarly, allelic richness explained a significant proportion of age/size variation (model: range(mm)/SD = log10(hectares)+Ar; p = 0.026 and 0.020). Though explaining some of the variation, the effect of habitat area was not significant in any of the four models (p>0.2), and this variable was excluded from the model fits for illustration purposes. The univariate relationships between these two measures of genetic diversity and two indicators of demographic diversity in goby populations are shown in Figure 3.

Mentions:
We detected a correlation between the temporal extent of the reproductive season and genetic diversity. A significant proportion of the variation in demography (as measured by observed size ranges and SD) was explained by expected heterozygosity (p = 0.018 and 0.022, respectively) after accounting for the effects of habitat area in a general liner model analysis (model: range(mm)/SD = log10(hectares)+HE). Similarly, allelic richness explained a significant proportion of age/size variation (model: range(mm)/SD = log10(hectares)+Ar; p = 0.026 and 0.020). Though explaining some of the variation, the effect of habitat area was not significant in any of the four models (p>0.2), and this variable was excluded from the model fits for illustration purposes. The univariate relationships between these two measures of genetic diversity and two indicators of demographic diversity in goby populations are shown in Figure 3.

Bottom Line:
We illustrate that, for this annual species, continuous reproduction is a safeguard against reproductive failure by any one population segment, as natural, stochastically driven salinity increases frequently result in high mortality among juvenile individuals.Notably, we found a significant correlation between genetic diversity and demographic variation in the study populations, which could be the result of population stressors that restrict both of these diversity measures simultaneously, or suggestive of a causative relationship between these population characteristics.These findings demonstrate the importance of biocomplexity at the population level, and assert that the maintenance of diversity contributes to population resilience and conservation of this endangered species.

Affiliation:
Department of Fisheries Biology, Humboldt State University, Arcata, California, United States of America; FISHBIO, Chico, California, United States of America.

ABSTRACTTheoretical work has shown that reduced phenotypic heterogeneity leads to population instability and can increase extinction potential, yet few examples exist of natural populations that illustrate how varying levels expressed diversity may influence population persistence, particularly during periods of stochastic environmental fluctuation. In this study, we assess levels of expressed variation and genetic diversity among demographically independent populations of tidewater goby (Eucyclogobius newberryi), show that reductions in both factors typically coincide, and describe how low levels of diversity contribute to the extinction risk of these isolated populations. We illustrate that, for this annual species, continuous reproduction is a safeguard against reproductive failure by any one population segment, as natural, stochastically driven salinity increases frequently result in high mortality among juvenile individuals. Several study populations deviated from the natural pattern of year-round reproduction typical for the species, rendering those with severely truncated reproductive periods vulnerable to extinction in the event of environmental fluctuation. In contrast, demographically diverse populations are more likely to persist through such periods through the continuous presence of adults with broader physiological tolerance to abrupt salinity changes. Notably, we found a significant correlation between genetic diversity and demographic variation in the study populations, which could be the result of population stressors that restrict both of these diversity measures simultaneously, or suggestive of a causative relationship between these population characteristics. These findings demonstrate the importance of biocomplexity at the population level, and assert that the maintenance of diversity contributes to population resilience and conservation of this endangered species.